Governor Jeb Bush has written to his brother, President George Bush, asking him to suspend federal environmental regulations which ensure that Florida has safe drinking water.

Rapid population growth in the low-lying state, which now has 16 million inhabitants and low levels of underground fresh water, will cause a serious risk of water shortages in Florida unless the restrictions are lifted, Governor Bush says.

State officials want to allow billions of gallons of untreated and partly contaminated rain and river water to be injected underground to help form underground reservoirs.

Such action would save Florida millions of dollars in water treatment costs, although officials say "extensive precautions" would be taken to avoid any health danger.

If the plan goes ahead, however, the federal government's environmental protection agency would have to waive rules which require that any water pumped into the ground must first be treated to meet drinking water standards.

In his letter, Jeb Bush called the requirement "nonsensical". He said the stored water would be treated before it was fed into the drinking water system and asked for "a willingness to abandon conventional processes as long as the environmental results are achieved".

Opponents say the governor's plan risks feeding untested water into private wells, where drinking water is not always treated and that the pumping process risks creating unforeseen hazards.

"This is something that really has not been studied yet with respect to the injection of untreated surface water. I think the state could be opening the door to a lot of problems," said John Vecchioli of the US geological service.

Florida's population is projected to reach more than 20m by 2020 and experts say that the state faces a water deficit of up to 30 per cent by then.

The state has suffered a succession of droughts, the worst in half a century.